The use of 4-phenylazopyrazolone masking couplers is known in the art. See, for example, U.S. Pat. Nos. 2,428,034; 2,434,272; 2,455,170; 2,688,539; 2,704,711; 2,808,329; 3,476,560; 3,796,574; 4,427,763; 4,777,123, and EP 213,490; as well as those identified in Research Disclosure December 1989, Section VII, Part G, Publiched by Kenneth Mason Publications, Ltd., Dudley Annex, 12A North Street, Emworth, Hampshire P010 7DQ, England. These compounds have proven useful since they are, subsequent to development, typically yellow colored in nonexposed areas and magenta colored in exposed areas. Thus, when in reality the magenta dye formed in a color negative photographic process has a small but significant unwanted absorption in the blue range, this may be balanced somewhat by the relative loss of blue absorption due to conversion of the mask color from yellow to magenta in the exposed areas. Then, an adjustment can be made to the spectral content of the light used to produce the positive from the negative to effectively cancel out the unwanted blue absorption, which is now relatively constant across both the exposed and unexposed areas of the negative.
While phenylazopyrazolone masking couplers have been employed as a means of offsetting the unwanted blue absorption of conventional magenta couplers, this means for improving the color rendition has now been found to be responsible for the degradation during raw stock keeping of bicyclic azole image couplers with corresponding losses in contrast, optical density and related photographic characteristics. The presence of these masking couplers results in the degradation and loss of image coupler. This is thought to be due to an undesired reaction in the raw stock prior to development between the masking coupler and undesired oxidants. The unwanted degradation of the image coupler eventually results in the loss of density in the photographic image. It is undesirable to have a film where the image density will vary with the length of raw stock storage time.
European Patent Application 232,101 discloses a photographic element containing a pyrazolotriazole coupler together with at least 17 mole % of a colored masking coupler which may be of the azopyrazolone type. The presence of the large relative percentage of the masking coupler is said to improve sharpness and grain. There is no suggestion of the advantages to be obtained by including a stabilizing coupler and, in fact, the higher concentration of masking coupler suggested would serve to aggravate the raw stock keeping problems. U.S. Pat. No. 4,777,123 contains a similar general disclosure but again does not suggest the advantage of using a stabilizing coupler. U.S. Patent 4,600,688 proposes broad combinations of pyrazolotriazoles and pyrazolones as having an advantageous color absorption spectrum. The specific combination of a bicyclic azole coupler, an azopyrazolone masking coupler, and a magenta dye-forming stabilizing coupler are not suggested nor is the resultant advantage in raw stock keeping afforded by:such combination recognized. European Patent Application 467,327 suggests the combination of a coupler similar to the stabilizing coupler of the invention having a particular nitrogen substituent with a bicyclic azole. According to the inventors, this combination may be used with all those materials conventionally used in photographic elements, any of various types of colored couplers for correcting unwanted absorption being among these. There is no recognition of the keeping problem associated with the combination of a bicyclic azole and an azopyrazolone masking coupler, no suggestion of the particular combination of the invention, and no suggestion of the improved keeping to be obtained with the inventive combination.
It would be desirable to provide a photographic element and process where an azopyrazolone masking coupler can be used in combination with a bicyclic azole image coupler without incurring degradation of the image coupler during raw stock keeping.